| 摘要 |
PROBLEM TO BE SOLVED: To ensure the safety of an earth drill and to improve the quality of a pile, by preventing erroneous operation of an operating lever of the earth drill. SOLUTION: Pilot passages 25 and 26 of a remote-control valve 24 operated by the operating lever 16 are connected to switch valves 27 and 28, respectively, which are then switched by a change-over switch 19, whereby pilot oil in the remote-control valve 24 is guided either to pilot ports 29 and 30 of a boom derricking control valve 21 or to pilot ports 31 and 32 of a kelly bar rotation control valve 22. In this manner, derricking operation of a boom 4 and rotating operation of a kelly bar 8 can be selectively carried out by the single operating lever 16.
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